The present invention relates to adhesive strips, and more particularly, to the art of disposable diapers that have a reinforced fastening area, i.e., the area of the diaper to which an adhesive tape is pressed to fasten the diaper around an infant or other person. The adhesive fastening tape is formulated to be sufficiently tacky to hold the tape securely in place while in storage, and to insure against undesirable release once a diaper is put on an infant.
Disposable garments such as diapers generally comprise a liquid permeable inner layer, a liquid impermeable out layer or back sheet and an absorbent batt secured between the liner and backing sheet. The inner liner may be any soft, flexible, porous sheet through which fluid may pass, and the inner liner may be comprised of a non-woven web or sheet of polyolefin fibers such as polypropylene, wet strength tissue paper, a spun-woven filament sheet, etc. The liquid impermeable outer sheet may be comprised of a thin web or sheet of polyolefin or plastic film material such as polyethylene, polypropylene, polyvinylchloride, etc. The absorbent batt may be comprised of any suitable absorbent material. Typically, the batt is comprised of a cellulosic material, such as air-formed batt of wood pulp fiber commonly known as "fluff."
The fastener tape closure systems used in disposable articles such as diapers include a pressure-sensitive adhesive tape tab attached at selected locations of the article such as at each of the two corners located at one end of the diaper. The unattached portions of the adhesive fastener tape tabs are configured to adhesively engage with the outer layer of the article at locations on other portions of the article. For example, the attachment zones for the fastening tape tabs are typically located at the opposite end of a diaper.
Releasable and refastenable tape tabs and tape tab closure systems are desired to allow the articles such as a diaper to be removed and refitted. For example, it often is desired to loosen or remove the diaper to determine if it is wet or to remove the diaper to bathe the infant. If the diaper has not been soiled, it can be reused.
The adhesive tape tabs employed tl fasten a diaper in a closed position, however, have to be fairly aggressive to provide an adhesive bond adequate to secure the waist portions of the diaper together. The adhesive bond strength generally is greater than the tensile strength and tear resistance of the materials comprising the impermeable outer layer or backing sheet. As a result, when the fastening tape tab is released or peeled from the diaper, the outer layer or backing sheet may tear away from the diaper whereby the diaper cannot be reused because the fastening tape cannot be reused. This problem occurs in part because the outer layer generally is a thin film of polymer material to reduce the weight and the cost of the disposable article. Therefore, when attempts are made to remove or reposition the adhesive fastening tape tab, the forces applied are sufficient to tear the outer polymer film of the diaper.
Various attempts have been made to provide releasable and reusable fastening tapes and tape closure systems. For example, attempts have been made to modify the aggressiveness or bonding strength of the adhesive used to form the adhesive tape. Another solution to this problem would be to use thicker, stronger and more tear-resistant materials as the outer layer, but this solution significantly raises the cost of the article increase the weight of the article and generally decreases softness and flexibility of the garment.
Proposals have been made to resolve these problems by reinforcing the area of the article which receives the adhesive fastening or closure tape. This area of the diaper to which the fastening tape is bonded when the diaper is applied is referred to in the industry as the "target zone" or "landing zone." In U.S. Pat. No. 4,643,730, the landing zone of the outer layer of a diaper is reinforced by coating that area of the outer layer (i.e., the area ultimately receiving the adhesive closure tape) with a layer of material that is curable by high-energy radiation. The cured coating forms a reinforcement layer affixed to the outer layer of the article. The radiation-curable compositions include at least one compound selected from the group consisting of urethane acrylate acrylic oligomers, acrylated acrylic oligomers and epoxy acrylate acrylic oligomers. The compositions also may contain monofunctional acrylate monomers, difunctional acrylate monomers, acrylic monomers and trifunctional acrylate monomers.
U.K. Patent 2,129,689 describes diapers which are provided with a non-elastic plastic strip in the region for fastening the tape tabs. The plastic strips are typically polyester, polyethylene, or polypropylene having a tear strength greater than the outer layer of the diaper. Since the plastic strip is non-elastic, there is no stretching when the fastening tab is removed from the strip.
U.S. Pat. No. 4,710,190 (Wood et al) discloses the use of a bilayer film as a reinforcing film for the outer layer of disposable diapers. The bilayer film comprises a reinforcing layer and a room temperature non-tacky bonding layer which will soften and bond at comparatively low temperatures of less tand about 115-120.degree. C. Because the adhesive is non-tacky at room temperature (non-blocking), the bilayer film is windable into a storage roll in which under normal storage conditions of about 50-60.degree. C. or less, the over-lying portions of the bilayer film do not become adhered together so as to resist uniform low-force unwinding. When applied to a substrate (such as a diaper) and subjected to heat and pressure, the bilayer film is bonded to the substrate in a peel-resistant manner so that the adhesive fastening tape tabs may be strongly adhered to the fastening area by simple hand pressure and held to the diaper without cohesive or other failure of the reinforced portion of the diaper. In addition, the patentees suggest that the fastening tape tabs may be removed and reapplied without distortion or tearing of the outer layer of the diaper.
U.S. Pat. No. 5,026,446 (Johnston et al) describes disposable diapers having target strips wherein the target strips are cut from a pressure-sensitive adhesive tape. The tape has a backing that has a low-adhesion backsize coating on its non-adhesive face, and at least part, but not all, of the low-adhesion backsize coating is removed with an abrasive to improve the adhesion thereof to pressure-sensitive adhesive tape tabs. A number of low-adhesion backsize coatings are described in Col. 2, and these include urethane backsizes as described in U.S. Pat. No. 2,532,011; fluorochemical backsizes such as fluorochemical acrylates as described in U.S. Pat. No. 4,472,480, and ultraviolet light curable silicone backsizes such as described in U.S. Pat. No. 4,530,879. At least 20% of the backsize coating is removed by the abrasive strip.
U.S. Pat. No. 5,106,383 (Mulder et al) describes disposable articles such as diapers containing a closure system comprising a film substrate having a target strip and a fastening tape. The target strip comprises a backing film having a first pressure-sensitive adhesive on one face thereof adhered to the film substrate, and on the other face thereof, a hydrophobic polyvinyl carbamate release coating. The fastening tape tabs have a pressure-sensitive adhesive on one face thereof for adhesion to the target strip. The target strip release coating is subjected to ionizing plasma treatment such that the fastening tape has an increase in adhesion to the target strip of at least about 50% over untreated target strips.